Sheet feeding apparatus

ABSTRACT

A sheet feeding apparatus which delivers successive topmost sheets of a stack of sheets into the range of advancing rolls in an electrostatic copying machine has a sheet feeding device using a cylindrical sleeve consisting of elastomeric material with a high coefficient of friction and and bearing against the topmost sheet of the stack. The sleeve is rotated intermittently by a drive in a direction to move the leading portion of the topmost sheet over a front stop and two corner separators into the range of the advancing rolls. Once the topmost sheet is engaged by the advancing rolls, it begins to rotate the sleeve because it is moved forwardly at a speed exceeding the peripheral speed of the sleeve under the action of its drive. The sleeve becomes disengaged from the topmost sheet in a predetermined angular position in which its lowermost point is still located above the topmost sheet. This insures that the sleeve cannot simultaneously engage the trailing portion of the topmost sheet and the nextfollowing sheet of the stack. The disengagement of the sleeve from the topmost sheet is effected by a steel roller which orbits about the axis of the sleeve and engages the topmost sheet in the predetermined angular position of the sleeve. The roller is attached to a disk which is secured to and rotates with a metallic core surrounded by the sleeve.

United States Patent 1191 Eppe et al. Feb. 18, 1975 SHEET FEEDING APPARATUS [75] Inventors: Rudolf Eppe, Taufkirchen; Karl ABSTRACT Hal-twig Umerhachmg; Juergen A sheet feeding apparatus which delivers successive vossnacke puuach of Germany topmost sheets of a stack of sheets into the range of [73] Assignee: Agfa-Gevaert Aktiengesellschaft, advancing T0115 in an electroslatlfi py machine Leverkusen, Germany has a sheet feeding device using a cylindrical sleeve consisting of elastomeric material with a high coeffi- [22] Flled: 1972 cient of friction and and bearing against the topmost [21 APPL 301, 01 sheet of the stack. The sleeve is rotated intermittently by a drive in a direction to move the leading portion of the topmost sheet over a front stop and two corner [30] Foregn Apphcat'on Prmr'ty Data separators into the range of the advancing rolls. Once Oct. 30, 1971 Germany 2154223 the topmost sheet is engaged by the advancing rolls, it

begins to rotate the sleeve because it is moved for- [52] US. Cl. 271/119, 271/116 wardly at a speed exceeding the peripheral speed of [5 l] Int. Cl B65h 3/06 the leeve under the action of its drive The sleeve be- Field of Search comes disengaged from the topmost sheet in a prede- 1 10 termined angular position in which its lowermost point is still located above the topmost sheet. This insures References Cited that the sleeve cannot simultaneously engage the trail- UNITED STATES PATENTS ing portion of the topmost sheet and the next- 1,133,024 3/1915 Hawkins 271/114 following Sheet ofthefltack- Thefiisengagemem Ofthe 2 764 409 9 195 LaBombard I 271/116 sleeve from the topmost sheet is effected by a Steel 2,996,862 8/1961 Johnson et al,., 271 115 UX roller which orbits about the axis of the sleeve and en- 3,294,019 12/1966 Taylor 271/114 X gages the topmost sheet in the predetermined angular 3,532,423 10/1970 Bruning a 7 X position of the sleeve. The roller is attached to a disk Primary Examiner-Evon C. Blunk Assistant Examiner-Bruce H. Stoner, Jr. Attorney, Agent, or Firm-Michael S. Striker which is secured to and rotates with a-metallic core surrounded by the sleeve.

5 Claims, 5 Drawing Figures 1 SHEET FEEDING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to apparatus for feeding successive topmost sheets of a stack of sheets lengthwise into and along a predetermined path, for example, into an electrostatic copying machine. More particularly, the invention relates to improvements in that device of a sheet feeding apparatus which engages and displaces successive topmost sheets of a stack of sheets so as to move theleading portions of successive topmost sheets into the range of advancing rollers or analogous transporting means which take over and continue the transport of sheets along the predetermined path. Still more particularly, the invention relates to improvements in intermittently driven rotary sheet feeding devices which are used in sheet feeding apparatus to engage successive topmost sheets of a stack of sheets and to move the leading portions of successive topmost sheets. beyond the customary corner separators and/or front stops and into the range of preferably constantly driven sheet advancing or transporting means.

ln presently known sheet feeding apparatus, the topmost sheet of a stack of sheets on a platform or an analogous carrier is engaged and displaced by a feeding device in the form of a feed roll which is provided with a peripheral layer consisting of elastomeric material and having a high coefficient of friction. The drive means for the feed roll includes an overrunning clutch which rotates the feed roll during the first stage of a sheet feeding cycle. Once the leading portion of the topmost sheet which is being displaced by the feed roll reaches the advancing rolls, the sheet begins to rotate the feed roll because the speed of the sheet increases as soon as it is moved into the range of the advancing rolls. Such rotation of the feed roll under the action of the rapidly advancing sheet terminates as soon as the trailing edge of the sheet moves beyond the point of contact with the periphery of the feed roll. The latter thereupon bears against the next'to-the-topmost (second) sheet and its inertia suffices to cause at least'some lengthwise displacement of the second sheet with the result that the leading edge of the second sheet is deformed or otherwise damaged by the front stop and/or by the corner separators. As a rule, the feed roll contacts the second sheet even before it becomes disengaged from the topmost sheet because the elasticity of its peripheral por tion and the force with which it bears against the topmost sheet-are high enough to insure that the feed roll elastic element.

Another object of the invention is to provide the apparatus with a novel and improved sheet engaging and feeding device and with novel means for automatically disengaging the elastic element of the feeding device from the topmost sheet of the stack in a predetermined angular position of the feeding device.

A further object of the invention is to provide a sheet feeding apparatus which insures that the sheet or sheets below the topmost sheet of a stack cannot be deformed and/or otherwise damaged during removal of the topmost sheet.

An additional object of the invention is to provide a sheet feeding apparatus which is particularly suited for use as a means for delivering successive sheets of a stack of sheets into an electrostatic copying machine wherein the sheets receive powder images.

Still another object of the invention is to provide a sheet feeding apparatus which can be used for transport of relatively thick, relatively thin, long, short, readily flexible or relatively stiff sheets without any damage to the sheets located below the sheet which is in the process of being moved off the stack.

The invention is embodied in a sheet feeding apparatus which is particularly suited for transporting successive topmost sheets of a stack of sheets into the range is deformed to an extent'which suffices to bring about machine which is to receive successive sheets from a stack.

SUMMARY OF THE INVENTION An object of the invention is to provide a novel and improved sheet feeding apparatus wherein the deformable elastic element of the rotary device which bears against the topmost sheet of a stack of sheets is automatically disengaged from the topmost sheet before the of sheet advancing rolls in an electrostatic copying machine whereby the leading portions of successive sheets must bypass corner separators and/or a front stop located between the stack and the advancing rolls. The sheet feeding apparatus comprises a carrier (e.g., a platform) for a stack of sheets including a topmost sheet, a rotary feeding device including an elastically deformable preferably sleeve-like element having a pcripheral surface which normally bears against the topmost sheet of the stack on the carrier with a predetermined force, and means for intermittently rotating the feeding device about the axis of the deformable element'so that the latter moves the topmost sheet lengthwise. The feeding device further includes a member which is arranged to disengage'the peripheral surface of the deformable element from the topmost sheet of the stack on the carrier in a predetermined angular position of the feeding device, namely, before the topmost sheet has been advanced to a position in which the deformed element could simultaneously engage the trailing edge of the topmost sheet and an intermediate portion of the next-following sheet.

The deformable element preferably consists of a material having a high coefficient of friction, and the dis engaging member may constitute or may include a relatively small roller whose axis is parallel to the axis of the deformable element and which engages the topmost sheet in the predetermined angular position of the feeding device.

In accordance with a further feature ofthe invention, the line connecting the axis of the deformable element with the axis of the disengaging roller and the line including the axis of the deformable element and being normal to the plane of the topmost sheet of the stack on the carrier make (in the predetermined angular position of the feeding device) an angle alpha which satisfies the equation wherein M is the moment of frictional resistance of v the roller, M A is the moment of frictional resistance of the deformable element, P is the force with which the.

deformable element normally bears upon the topmost sheet of the stack on the carrier, r is the radius of the roller, and r is the distance between the axes of the deformable elementand the roller.

The feeding device may further include a second roller which also engages the topmost sheet of the stack on the carrier in the predetermined angular position of the feeding device to further insure that the deformable element is out of contact with the topmost sheet before the trailing portion of the topmost sheet advances beyond the region of contact with the deformable element.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved sheet feeding apparation has been removed from the body of the elastic tus itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a fragmentary side elevational view of a portion of a conventional sheet feeding apparatus;

FIG. 2 is a fragmentary side elevational view of a sheet feeding apparatus which embodies one form of DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a portion of a conventional sheet feeding apparatus whereinan elastic feed roll 3 is in the process of moving the topmost sheet 2 of a stack 1 in the direction indicated by arrow C. The roll 3. bears against the stack 1 with a force P which can be generated by biasing the feed roll 3 downwardly toward the stack 1 or by urging the stack upwardly against the feed roll. For example, the carrier or platform 50 which supports the stack 1 can be biased upwardly under the action of one or more weights suspended on cables, passing over suitable pulleys, or the platform 50 for the stack 1 can be urged upwardly by one or more springs.

FIG. 1 illustrates that stage of forward transport of the topmost sheet 2 when the feed roll 3' (which is driven intermittently to rotate in the direction indicated by arrow Alengages the trailing portion 2a of the topmost sheet 2 as well as the adjacent intermediate portion of the next-following second sheet 2A. The deformability of the feed roll 3 is amply sufficient to insure that the feed roll simultaneously engages the sheets 2 and 2A. Due to its engagement with the sheet 2A, the feed roll 3 causes this sheet to move forwardly and to have its leading portion deformed by conventional corner separators such as those shown at 17, 18 in FIG. 5. The leading portions of successive sheets are caused to enter the nip of two advancing rolls (such as the rolls 14, 15 of FIG. 5) which thereupon transport the sheets through an electrostatic copying or other machine wherein or in combination with which the sheet feeding apparatus is being put to use.

FIGS. 2 and 3 illustrate a portion of a sheet feeding apparatus which is constructed and assembled in accordance with a first embodiment of the invention. The rotary sheet feeding device comprises ashaft 6 which supports a cylindrical metallic core 19 surrounded by a sleeve-like elastic element 3 (hereinafter called sleeve) having axially parallel peripheral ribs to enhance its sheet feeding action. A segment-shaped porsleeve 3 so that the latter exhibits a flat 30 located in a plane which is parallel to the axis of the shaft 6. The core 19 or the shaft 6 carries a disk 20 provided with an eccentric pin or shaft 4 for a disengaging member here shown as a-small roller 5 which is held against axial movement away from'the disk 20 by a split ring 21. As shown, a portion of the disengaging roller 5 extends beyond the flat 3a of the elastic sleeve 3. The roller 5 may consist of steel and is preferably provided with a highly polished cylindrical peripheral surface. The material of the sleeve 3 has a high coefficient of friction. 1

The sleeve 3 is assumed to feed the topmost sheet 2 of the stack 1 on the platform or carrier 50 in the direction indicated by arrow C. In the angular-position of the sheet feeding device shown in FIG. 2, the leading edge portion K of the flat 3a engages the upper side of the topmost sheet 2 simultaneously with the peripheral surface of the disengaging roller 5. The leading portion of the topmost sheet 2 is assumed to have moved into and beyond the nip of the advancing rolls 14, 15 shown in FIG. 5 so that the sleeve 3 is rotated by the advancing rolls by way of the sheet 2. The arrow A indicates the direction of rotation of the sleeve 3. If the sleeve 3 were to rotate beyond the angular position shown in FIG. 2, the edge portion K would be lifted off the upper side of the topmost sheet 2. This can take place (i.e., the sheet feeding device can assume a predetermined angular position in which the sleeve 3 is lifted off the sheet 2 by the roller 5) if the moment of rotation furnished by the roller 5 suffices, namely, if the various forces acting upon the sleeve 3 and roller 5 are related to each other in the following way:

The moment of rotation acting upon the sleeve 3 in PL MG/I'G.

The maximum moment of rotation which tends to turn the sleeve 3 in the direction indicated by arrow A is My and can be expressed as follows:

My M r COSa/r The moment of rotation M which tends to rotate the sleeve 3 counter to the direction indicated by arrow A is determined by the force P which equals r times sin a. This moment of rotation can be expressed as follows:

It is further necessary to overcome the moment M A of I frictional resistance of the sleeve 3. The condition for a standstill of the sleeve 3 can be expressed by the following equation:

M 5 M r cosa/r P .r sina wherein sin a Z l/P (M cosoz/r M /r By proper selection of the angle a which is a function of r and r it is possible to invariably prevent further rotation of the sleeve 3 beyond the position shown .in FIG. 2. As the topmost sheet 2 continues to move in the direction indicated by arrow C, it merely rotates the disengaging roller 5 whose deformability is minimal or non-existent and whose external surface is sufficiently smooth so that its coefficient of friction is also negligible. Consequently, the diverging rollerS cannot entrain the second sheet 2A when the trailing portion of the topmost sheet 2 has been advanced beyond the lowermost point on the peripheral surface on the disengaging roller 5. It is further possible to select the magnitude of the angle a in such a way (i.e., to make this angle so small) that the sleeve 3 is prevented from rotation beyond the position of FIG. 2 and that the pressure which the edge portion K exerts upon the topmost sheet 2 is much smaller than the pressure previously exerted by the preceding part of the periphery of the sleeve 3. this insures that the wear on the edge portion K is minimal so that the sleeve 3 can stand long periods of use.

It will be noted that the angle a is enclosed by a line which connects the axes of the sleeve 3 and disengaging roller 5 and a line which includes the axis of the sleeve 3 and is normal to the plane of the topmost sheet 2 of the stack of sheets on the carrier or platform 50.

The wear upon the edge portion K can be completely eliminated if the sheet feeding device of the apparatus.

is constructed in a manner as illustrated in FIG. 4 wherein the disk carries two cylindrical rollers 5 and 7. The shaft for the roller 7 is shown at 8. The roller 5 is rotatable on or with its shaft 4 with a minimum of friction. On the other hand, the roller 7 offers a much higher resistance to rotation about its axis (with or relative to the shaft 8). It is even possible to fixedly mount the shaft 8 in the disk 20 and to fixedly secure the roller 7 to the shaft 8. The line connecting the axes of the shafts 4, 6 makes with the line connecting the axes of the shafts 6, 8 an angle 2 a. This angle is halved by the direction in which the force P acts when the peripheral surfaces of the rollers 5 and 7 engage the upper side of one and the same sheet of the stack 1 (e.g., the illustrated topmost sheet 2). i

The roller 7 should offer a relatively high resistance to rotation about its axis because, otherwise, the sleeve 3 would turn only to the angular position shown in FIG. 5 in which the edge portion K of the flat 3a continues to abut against the topmost sheet 2 and slides therealong as the latter is being pulled by the advancing rolls l4 and 15. Furthermore, the sleeve 3 would have to complete a relatively large angular movement in the direction of arrow A prior to starting with the feed of the second sheet 2A in order to move the edge portion K into engagement with the upper side of the sheet 2A and to transport the latter into the range of the advancing rolls l4, 15.

Were the sleeve 3 to turn beyond the angular position shown in FIG. 4 under the action of the topmost sheet 2 which is being pulled by the rolls 14, 15, the roller 7 would have to be lifted off the sheet 2. This is prevented by the moments of rotation which were described in connection with FIG. 2. Thus, there develops a moment which tends to rotate the sleeve 3 in the directionof arrow A and which is due to the action of the force P, upon the lever arm r times cos a. Furthermore, there develops a moment which tends to rotate the sleeve 3 in a direction counter to that indicated by the arrow A and is determined by the force P acting on the lever arm r 'times sina. The difference of the two moments tends to overcome the moment M of frictional resistance of the sleeve 3.

It will be noted that the roller 7, which offers greater resistance to rotation about the axis of the shaft 8, is located ahead of the roller 5 (which offers lesser resistance to rotation about the axis of its shaft 4) as considered in the direction (arrow A) of rotation of the deformable sleeve 3 in order to move the sheets 2, 2A, etc. into the range of the advancing rolls 14 and 15. Due to its high resistance to rotation about the axis of the shaft 8, the roller 7 causes the sleeve 3 to turn about the axis of the shaft 6 until the topmost sheet 2 is simultaneously engaged by the peripheral surfaces of the rollers 7 and 5. The line including the axis of the sleeve 3 and halving the shortest distance between the axes of the rollers S and 7 is then normal to the plane of the sheet 2, i.e., such line coincides with the normal direction of pressure of the sleeve 3 upon the sheet 2.

If the angle alpha is selected in a manner as described in connection with FIGS. 2 and 3, the feeding device of FIGS. 4 and 5 is automatically held against further rotation in the direction of arrow A as soon as the peripheral surface of the roller 5 comes into contact with the topmost sheet 2, i.e., when the feeding device assumes the predetermined angular position of FIG. 5. By properly selecting the angle alpha, one can greatly reduce 1 the pressure with which the roller 7 bears against the sheet 2 and hence the frictional resistance which the roller 7 offers to lengthwise transport of the sheet 2 under the action of the advancing rolls 14 and 15. Since the feeding device reaches the predetermined angular position of FIG. 5 when the sheet 2' is engaged by the roller 7 as well as by the roller 5, the angular movement which is necessary to move the sleeve 3 into frictional engagement with the sheet 2A (upon completed movement of the sheet 2 beyond the range of the sleeve 3) is relatively small. 7

The provision of the flat 3a on the peripheral surface of the sleeve 3 insures that the angle alpha (which determines the moment tending to rotate the sleeve 3 counter to the direction indicated by the arrow A) can be relatively large without risking a contact between the sleeve 3 and the sheet 2 in the space between the rollers 5 and 7.

FIG. 5 further shows the manner in which the sleeve 3 is driven to transport successive sheets 2, 2A, etc., of

the stack 1 into the nip of the advancing rolls 14,15. The core 19 carries a gear 13 which meshes with a gear segment 12a provided on a lever 12 fulcrumed at 12b. The lever 12 is articulately connected with a rod 11 which is reciprocated by a crank or cam, not shown, to thereby pivot the lever 12 back and forth. The gear 13 can rotate the sleeve 3 in the direction of arrow A through the intermediary of an overruning clutch 13a. When the lever 12 pivots clockwise,the gear 13 rotates the sleeve 3 in a counterclockwise direction by way of the clutch 13a whereby the peripheral surface of the sleeve 3 feeds the topmost sheet 2 in the direction of the arrow C and into the range of the advancing rolls 14, 15. During movement in the direction of arrow C, the topmost sheet 2 causes its front corner portions to flex and to thus bypass the corner separators 17, 18. Such bypassing of the corner separators 17, 18 is facilitated by the provision of a front stop 16 against which the front edges of the sheets forming the stack 1 abut. As the sleeve 3 pushes the topmost sheet 2 forwardly, the center of the foremost partof such sheet bulges upwardly immediately behind the front stop 16 and the corner portions move above and beyond the corner separators 17, 18.

As soon as the frontportion of the sheet 2 is engaged and entrained by the advancing rolls 14, 15, the sheet 2 begins to rotate the sleeve 3 atan elevated speed so that the sleeve continues to rotate in the direction of arrow A. This is made possible by the provision of the overrunning clutch 13a. At the same time, the lever 12 continues to pivot in a clockwise direction under the action of the rod 11. The angular movement of the sleeve 3 in the direction of arrow A is terminated when the topmost sheet 2 is engaged by the disengaging roller The axial length of the sleeve 3 is normally substantially less than the width of a sheet. If desired, the shaft 6 can carry two or more coaxial elastic sleeves 3. If the shaft 6 carries a single sleeve 3, the latter is located centrally of the stack 1, i.e., midway between the longitudinally extending marginal portions of the sheet 2. If

. the shaft 6 carries several sleeves 3, they are preferably distributed uniformly across the width of the topmost sheet 2. An important advantage of the improved sheet feed ing apparatusis that it preventsethe sleeve or sleeves 3 from flexing or bulging the second sheet 2A while the topmost sheet 2 is being transported into the range of the advancing rolls l4, 15. In other words, the apparatus insures that the sheet 2A is not caused to bulge immediately behind the front stop 16 of FIG. in response to forward transport of the topmost sheet 2 and at that stage of forward transport of the sheet 2 when the sleeve 3 would normally engage the sheet 2A be hind the trailing edge of the sheet 2 (see the sleeve 3' of FIG. 1). Feeding of sheets without any deformation of the second sheet during forward transport of the topmost sheet is of particular importance in'electrostatic copying machines as well as in all such machines or apparatus wherein the sheets of a stack should be fed individually to one or more treating stations. In an electrostatic copying machine, the interval between the transport of a preceding sheet (2) and the transport of the next sheet (2A) can be relatively long so that, if the sheet 2A has been deformed in response to forward transport of the topmost sheet 2, the deformation of the second sheet is likely to be permanent due to the length of the interval which elapses before the sheet 2A is actually cairsedlq advance bgyond the front stgglfi and corner separators 17, 18.

Permanentdeformation of sheets which are fed into an electrostatic copying machine is particularly undesirable because each sheet must be brought into full surface-to-surface contact with the drum which carries the powder image. Such powder image must be transferred onto the sheet which is held in contact with the drum. Furthermore, the sheet with a powder image thereon must be transported through a fusing or fixing station and proper fusing of the powder image is either difficult or impossible if the sheet is permanently deformed before'it reaches the fusing unit. Eventual deformation of the leading portion of a sheet which is being transported from a stack into and through a copying or like machine is of lesser importance if the sheet is being transported by grippers which pull the sheet through one or more processing stations. In such feeding apparatus, the sheet is normally flattened due to the'pull of grippers so that even a permanent deformation might not be as damaging as when the sheet is being pushed by advancing rolls in a manner as illustrated in FIG. 5. l

The improved sheet feeding apparatus can be used with particularadv'antage in or with relatively small copying or like machine which are'not provided with sophisticated and hence expensive means for insuring accurate registry of successive sheets with various instrumentalities at one or more treating stations. Thus, a relatively large and complex printing, copying or like machine is invariably provided with adjustable corner separators, adjustable sheet feeding rolls, adjustable grippers and/or other means which receive successive sheets by simultaneous formation of compensating bulges in a manner well known from the art. However, even if the advancing means forsuccessive sheets is as simple as shown in FIG. 5, it is often desirable to feed successive sheets 2, 2A, etc. into the nip of the advancing rolls 14, 15 while forming each sheet with a compensating bulge and by using an electromagnet or the like to rapidly start the rolls l4, 15 at the exact moment 2 when the rolls are ready to move the leading edge of each sheet into the first treating station in an optimum position for transfer onto the sheet of a complete powder image or other information.

In-the embodiment of FIGS. 2 and 3, the distance r plus r need not exceed the radius of the round portion of the sleeve 3 so that the feeding 'device need not hobble in the course of the next-following rotation under the action of the lever ,11 in order to advance the second sheet 2A into the range of the rolls 14, 15. The same holds true for the rolls 5 and 7 of FIGS. 4 and 5.

However, it is equally within the purview of the invention-to use in the'improved feeding apparatus a sleeve 3 which does not have a flat 3a and which is associated with a disengaging roller 5 or with rollers 5, 7 in such a way that a portion of each roller extends beyond its preferably roughened peripheral surface. Such apparatus can employ a simpler sleeve but the operation of the feeding device involves some hobbling of the truly cylindrical sleeve due to the fact that the roller or rollers 5, 7 extend'beyond its peripheral surface.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. In a sheet feeding apparatus, particularly for transporting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separators and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of said element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a disengaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disengaging member including a roller having a portion extending beyond the peripheral surface of said element and an axis which is parallel to the axis of said element, said roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of saidfeeding device, the line connecting the axis of said element with the axis of said roller and the line including the axis of said element and extendng at right angles to the plane of the topmost sheet of the stack on said carrier making in said predetermined angular position of said feeding device an angle alpha which satisfies the equation sin a l/P (M cos a/r M /r wherein M is the moment of frictional resistance of said roller, M A is the moment of frictional resistance of said element, P is the bias of said element-upon the topmost sheet of the stack on said carrier, r is the radius of said roller, and r is the distance between the axes of said element and said roller.

2. A combination as defined in claim 1, wherein said peripheral surface of said element has a flat located in the region of sid disengaging member and facing the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device.

3. A combination as defined in claim 2, wherein said roller extends at least in part radially beyond said flat of said peripheral surface.

4. In a sheet feeding apparatus, particularly for transporting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separator and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of said element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a disengaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disengaging member including a first roller having a portion extending beyond the peripheral surface of said element and an axis which is parallel to the axis of said element, said first roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device and said feeding device further comprising a second roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device, the axis of said second roller being parallel to the axis of said first roller, at least one of said rollers being rotatable about the respective axis in response to engagement with the topmost sheet of the stack on said carrier and the opposition which said one roller offers to rotation about the respective axis being less than the opposition offered by the other of said rollers to rotation about the axis of said other roller.

5. In a sheet feeding apparatus, particularly for trans porting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separators and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of said element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a diseggaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disagaging member including a first roller having a portion extending beyond the pe ripheral surface of said element and an axis which is parallel to the axis of said element, said first roller enaging the topmost sheet of the stack on said carrier in said predetermined angular position of sid feeding device and said feeding device further comprising a second roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device, the axis of said second roller being parallel to the axis of said first roller, the lines respectively connecting the axis of said element and said first roller and the axes of said element and said second roller making an angle 2 alpha wherein the angle alpha satisfies the equation sin a l/P (M cosa M )/r r wherein M is moment of frictional resistance of said first roller, M A is the moment of frictional resistance of said element, Pg isthe bias of said element upon the topmost sheet of the stack on said carrier, r,; is the radius of said first roller and r is the distance between the axes of said element and said first roller. 

1. In a sheet feeding apparatus, particularly for transporting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separators and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of said element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a disengaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disengaging member including a roller having a portion extending beyond the peripheral surface of said element and an axis which is parallel to the axis of said element, said roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device, the line connecting the axis of said element with the axis of said roller and the line including the axis of said element and extendng at right angles to the plane of the topmost sheet of the stack on said carrier making in said predetermined angular position of said feeding device an angle alpha which satisfies the equation sin Alpha 1/PA (MGcos Alpha /rG - MA/rL), wherein Mg is the moment of frictional resistance of said roller, MA is the moment of frictional resistance of said element, PA is the bias of said element upon the topmost sheet of the stack on said carrier, rG is the radius of said roller, and rL is the distance between the axes of said element and said roller.
 2. A combination as defined in claim 1, wherein said peripheral surface of said element has a flat located in the region of sid disengaging member and facing the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device.
 3. A combination as defined in claim 2, wherein said roller extends at least in part radially beyond said flat of said peripheral surface.
 4. In a sheet feeding apparatus, particularly for transporting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separator and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of sid element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a disengaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disengaging member including a first roller having a portion extending beyond the peripheral surface of said element and an axis which is parallel to the axis of said element, said first roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device and said feeding device further comprising a second roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device, the axis of said second roller being parallel to the axis of said first roller, at least one of said rollers being rotatable about the respective axis in response to engagement with the topmost sheet of the stack on said carrier and the opposition which said one roller offers to rotation about the respective axis being less than the opposition offered by the other of said rollers to rotation about the axis of said other roller.
 5. In a sheet feeding apparatus, particularly for transporting successive topmost sheets of a stack of sheets into the range of sheet advancing means in an electrostatic copying machine whereby the leading portions of successive topmost sheets must bypass corner separators and front stops, a combination comprising a carrier for a stack of sheets including a topmost sheet; a rotary feeding device including an elastically deformable element having a peripheral surface normally bearing against the topmost sheet of the stack on said carrier, the material of said element having a high coefficient of friction; and means for rotating said device about the axis of said element so that said element moves the topmost sheet lengthwise, said feeding device further including a disagaging member arranged to disengage said peripheral surface of said element from the topmost sheet in a predetermined angular position of said feeding device, said disagaging member including a first roller having a portion extending beyond the peripheral surface of said element and an axis which is parallel to the axis of said element, said first roller enaging the topmost sheet of the stack on said carrier in said predetermined angular position of sid feeding device and said feeding device further comprising a second roller engaging the topmost sheet of the stack on said carrier in said predetermined angular position of said feeding device, the axis of said seCond roller being parallel to the axis of said first roller, the lines respectively connecting the axis of said element and said first roller and the axes of said element and said second roller making an angle 2 alpha wherein the angle alpha satisfies the equation sin Alpha 1/PA (MGcos Alpha MA)/rG rL, wherein MG is moment of frictional resistance of said first roller, MA is the moment of frictional resistance of said element, PA is the bias of said element upon the topmost sheet of the stack on said carrier, rG is the radius of said first roller and rL is the distance between the axes of said element and said first roller. 